Communication system



July 3, 1945. F. A. HUBBARD 2,379,715

COMMUNICATION SYSTEM Filed Oct. 9, 1942 7 Sheets-Sheet 1 /N M? N TOR I FRANCIS A. HUBBARD ATTORNEY F. A. HUBBARD COMMUNICATION SYSTEM Filed Oct. 9, 1942 7 Sheets-Sheet 2 INVENTOR FRANCIS A. HUBBARD MEM ATTORNEY EN Qw July 3. 1945.

F. A. HUBBARD 2,379,715

COMMUNICATION SYSTEM Filed Oct. 9, 1942 'r Sheets-Sheet 5 July 3, 1 945;

X. OW ///X /QQM M QK /N VEA/TOR FRA NC/S A. HUBBA R0 July 3, 1945. F. A. HUBBARD COMMUNICATION SYSTEM 7 sheets sheet 4 Filed Oct. 9, 1942 O w W MUM /U H M NM A T TORNEV F. ,A. HUBBARD COMMUNICATION SYSTEM July 3, 1945.

Filed 001;. 9, 1942 '7 Sheets-Sheet 5 lNl/ENTOR 5m /vc/s A. HUBBARD kf m at A T Tom/E July 3, 1945. A F. A. HUBBARD COMMUNICATION SYSTEM '7 Sheets-Sheet 6 Filed Oct. 9, 1942 V -A NP V m n m V W P NO M/HZQ/ m/vz/vroe FRANCIS A. HUBBARD ATTORNEY July 3, 1945. 1 HUBBARD 2,379,715

COMMUNICATION SYSTEM Filed Oct. 9, 1942 7 Sheets-Sheet 7 gill :IAWIIIIIII Ill/I'll!!! IIIIIIIIIIII /Nl EN TOR F RA NC/S A. HUBBARD By W 6% ATTORNEY Patented July 3, 1945 COMMUNICATION SYSTEM Francis A. Hubbard, Maplewood, N. J assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 9, 1942 Serial No. 461,428

19 Claims.

This invention relates to electrical switching methods and switching devices and particularly to these methods and devices when applied to communication systems.

The objects of the invention are to simplify the devices used to perform the switching of communication lines and other electrical circuits; to eliminate to a large extent the moving mechanisms heretofore used for this purpose; to reduce the number of switching stages necessary for the establishment of connections between communication'lines; to increase the speed with which connections may be established; and in other respects to obtain improvements in switching methods and devices.

Many varieties of automatic switching have been proposed in the past for interconnecting the lines of telephone, telegraph and other com- I munication systems. In almost all cases these of electromechanical devices in which moving parts serve to perform the selective and connecting operations involved in the establishment of the'desired connections. While some of these types have been developed to a high degree of reliability, it is true nevertheless that the presence of moving mechanical elements imposes limitations on the speed of operation and also introduces other problems. Also there have been a number of suggestions heretofore for the use of electron beams for selecting telephone lines and other similar circuits. Furthermore, it has been previously suggested to use electron. beams as distributors in systems of the usual multiplex distribution type. v

In accordance with the present invention improvements and advantages are obtained over these prior methods and arrangements by means of a switching system in which electrical connection may be established between any two lines in a group of lines by means of energy beams which are capable of being directed automatically and repeatedly into engagement with the desired lines. More specifically a group of lines, having an appearance in a scanning field as calling or incoming lines,'are scanned repeatedly at a high rate of speed by an energy beam, such as that produced by a cathode beam tube; and at the same time the said group of lines, having another appearance in a second scanning field as called or outgoing lines, are traversed by a second energy beam which is directed automatically into engagement with one line of a connecting pair whenever the first beam engages the other line of such pair. With this arrangement a pair of energy beams may serve to establish coexisting connections between a plurality of pairs of lines. To this end the first beam traverses the group of lines repeatedly and in a definite sequence, and

engaged in communication the second beam is directed automatically to the other line of the pair, and a momentary communication connection is established between the two lines. This operation is repeated in such rapid succession that the communication connection between each pair of lines is substantially continuous.

Another feature of the invention is a system in which the designations of the calling and called lines are registered and serve to control the scanning beams in such a way that one of these beams is automatically directed into engagement with one line of a. pair each time the other beam encounters the other line ofthe pair.

Another feature of the invention is a system in which auxiliary scanning beams are provided for controlling One of the two connecting beams in accordance with the designations of the calling and called lines. When one of the connecting beams engages the calling line, the auxiliary beams are simultaneously in positions to direct the other connecting beam to the called line in accordance with the digits thereof. Similarly, when thefirst connecting beam reaches the called line, the auxiliary beams are simultaneously in positions to direct the second connecting beam into engagement with the calling line. Thus the calling and called lines are in communicative engagement with each other for two-way transmission once per cycle of the scanning beams.

' These and other features of the invention will be discussed more fully in the following detailed specification. K

In the "drawings accompanying the specification Figs. 1 to 7, when arranged in the order illustratedin Fig. 8, disclose a telephone system in corporating the features of this invention.

Fig. 1 shows two of the subscribers lines, together with the line circuits and associated equipment; 7

Fig. 2 discloses a transmitting beam switch in which all of the lines appear and which serves to transmit the voice signals originating in all lines engaged in conversation;

Fig. 3 discloses a reproducer or connecting beam switch]: in which all of the lines appear and which serves" to transmit the voice signals to all lines engaged in conversation Fig. 4 discloses a pair of registers for registering the designations of the calling and called lines;

Fig. 5 shows a plurality of direction-controlling registers, the purpose of which is to control the scanning beam of the reproducer; Fig. 6 shows a beam device which acts under the control of the registers of Fig. 5 to direct the horizontal movement of the reproducer beam; and

each time it encounters one of thelines of a pair 5 Fig. '7 shows a similar beam device, the funcswitch 300.

tion of which is to control the reproducer beam in its vertical movement.

The invention in its broader aspects contemplates a multiplex system in which a plurality of communication channels are established concurrently for voice communication, telegraph signaling, or transmission of any other desired type. In the present disclosure, however, a telephone system has been chosen for the purpose of illustrating the invention. It is also assumed that there are 100 lines in this telephone system, some or all of which may be subscribers line, although it will be obvious that the invention is not so limited and that any desired number of lines may be included therein.

Referring to the drawings, it will be noted that each of the subscribers lines in the system appears at the central office in a transmissiontransformer of the hybrid type, whereby voice currents outgoing from the line and incoming thereto may be transmitted and received without mutual interierence. For example, subscribers line 100 appears in the hybrid transformer IM and balancing network 102 and line I03 appears in the hybrid transformer I04 and balancing network I05, and the same is true of each of the remaining lines in the system.

Each of the 100 lines in the system also has an individual appearance in the transmitting beam switch 200. To this end the beam switch is provided with a field of 100 lamps 20l, each of which represents and is connected'to one of the subscribers lines, these lamps beingarranged in a coordinate array of ten horizontal rows and ten vertical rows. The beam switch is also provided with an image screen 202 together with a suitable lens system for casting an image of the lamp array 20l on the screen 202. Accordingly, the screen 202 may be considered as comprising 100 elemental areas arranged coordinately in ten horizontal and ten vertical rows, said elemental areas corresponding to the lamps in the lamp field 20!. Moreover, the switch 200 is provided with means, such as an emitting cathode 3, f producing a beam of electrons, together with driving means 204 for causing the beam .to scan the screen 202 repeatedly at a high rate of speed and in accordance with a desired pattern. The beam switch 200 is not shown in full structural detail; however, it may be of any suitable type, well known in the art, in which the output voltage from the screen 202 created by the passage of the electron beam over'the successive elemental areas is directly proportionate to the amount of light focussed on said individual areas.

Besides appearing in the transmitting switch 200 the group of one hundred lines also appears in a scanning reproducer or beam connector The scanning field 301 of the reproducer 300 is divided into one hundred electrlcally separate elemental areas arranged coordinately in ten horizontal and ten vertical rows, and the lines are connected respectively to these elemental areas. The reproducer 300 is also provided with an electron emitting cathode 302 for producing a-beam of electrons, a driving device 303 for directing the beam over the scanning field 30l, a control electrode 304 for controlling the intensity of the beam, and a suppression electrode Sid for suppressing the beam while it is in transit from one elemental area to the next representing lines in conversation. Like the switch 200, the reproducer 300 may be of any suitable type. For example, any of the well-known cathode ray tubes may be employed, the general requirements being that the screen is divided into a field of electrically separate elemental areas of light-sensitive material, that a beam of electrons is provided for scanning the field of elemental areas, and that a beam-directing means is provided for driving the beam over the areas in a desired manner.

The horizontal and vertical location of the appearance of each line in the scanning field 202 of the transmitter and in the scanning field 3! of the reproducer is identical. Although any desired numbering system could be used, it will be as Sumed for the purpose of the present disclosure that the line appearances in the fields 202 and 30l are numbered from left to right and from top to bottom, beginning with the elemental area in the upper left corner of the field. For example, the first ten lines (lines No. 0 to No. 9) appear in the uppermost horizontal row of lamps in the field 20I of the transmitter and in the images of these lamps in the corresponding row of elemental areas in the field 202, numbered from left to right in both cases. Furthermore, these first ten lines appear through electrical connections in the uppermost horizontal row of elemental areas in the field 30| of the reproducer. The next ten lines (lines No. 10 to No. 19) appear in the second horizontal row of lamps 20! and correspondingly in the second horizontal row of image areas 202 of the transmitter and likewise in the second horizontal row of elemental areas in the field 30l of the reproducer. The third group of ten lines (lines No. 20 to No. 29) appear in the third horizontal row (from the top) of lamps in the field 20I and correspondingly in the third horizontal row of image areas in the field 202. Likewise this group of lines appears in the third horizontal row (from the top) of elemental areas in second horizontal row until it reaches the last area 208 therein, from whence it returns to the first area in the third horizontal row, and' so on until it has reached elemental area 209 in the field. At this time the beam returns to the beginning of its cycle and repeats the pattern. The potential for operating the beam driving means 204 is supplied by the oscillator 2l0. The frequency of the oscillator 2l0 determines the scanning frequency of the beam, which may be, for example, irom 6,000 to 10,000 frames per second. Thus the electron beam of the transmitting switch 200 scan repeatedly, and in rapid succession, and in numerical order, the appearances of the group of one hundred lines in the image field 202; and, as will be seen hereinafter,

. the numbers of the calling and called lines and a pair of beam devices 600 and which respond to these registrations for the purpose of controlling the horizontal and vertical motion components of the connector beam. The designation registering mechanism comprises a plurality of pairs of line finders and connector switches and also a plurality of individual line registers. The finder and connector registers may be of any suitable type, such as the well-known two-movement step-by-step switches commonly used in telephone systems.

The line finder 400 and the connector 40I constituting one of the register pairs, are common to the subscribers lines and may be taken in use to serve a calling line by any well-known allotment method. The line finder 400 in addition to its usual terminal banks and brushes is provided with a vertical commutator 402 and with a rotary commutator 403. The ten segments 'of the vertical commutator 402 are connected to resistors of graduated values, the value of each resistor representing the corresponding level and the tens digit of all lines appearing in that level. Similarly, the ten segments of the rotary commutator s03 are connected to ten resistors of graduated values, the value of each resistor representing the corresponding rotary position of the switch and the units digit of all lines appearing in that rotary position. The connector switch 40I is also provided with a vertical commutator 404 and with a rotary commutator 405; and the ten graduated resistors associated with the vertical commutator represent the ten values of the tens digit of the called lines, while the graduated resistors associated with the rotary commutator 405 represent the difierent values of the units digits of the called lines. Briefly stated, therefore, the automatic vertical and rotary movements of the line finder .400 performed in the act of finding a calling line serve to register the tens and units digits of the calling line number on the vertical and rotary commutators 402 and 403, respectively. And the vertical and rotary movements of the connector switch 40! in response to the calling subscriber, when he dials the number of the called line, serve to register the tens and units digits of the called line on the vertical and rotary commutators 404 and 405, respectively.

It'will be remembered that, the beam of the rection; and, when the magnet is energized by current of the opposite polarity, the armature 505 advances the idler pu1ley50l into engagement with the driving pulley 509 to move the brush 504 in the opposite direction. The operating windings of each pair of line register magnets are connected through the terminal banks of the lin finder and connector switches 400and 40I to the" vertical and rotary commutators of these switches in such a manner that the pair of line registers individual to each line of a conversational pair of lines are positioned automatically in accordance with the tens and units digits respectively of the other line of said conversational pair. If, for example, lines I00 and I03 are to be connected for conversation, the line registers 500 and 50I individual to the line I00 are positioned automatically in accordance with connector 300 is directed to the called line appearance each time the beam of the transmitter 200 scans the calling line and is directed to the calling line appearance each time the transmitter beam scans the called line. Therefore, the registration of the calling line number on the finder switch 400 must be utilized thorugh the controlling beam devices 600 and 100 to direct the cone nector beam to the called line at the proper instant; and the registration of the called line on the connector switch 400 must be utilized I through the controlling beam devices to direct the connector beam to the calling line appearance at the proper instant. To this end each subscriber's line is provided with a pair of beamcontrolling registers. Four of these registers are shown in Fig. 5, registers-500 and I being individual to line I00, and registers 502 and 503 being individual to line I03. Each of these line registers, such as the'register 500, comprises a the tens and units digits respectively of the line I03; and likewise the registers 502 and 503 of the line I03 are positioned automatially in accordance with the tens and units digits respectively of the line I00. As will be explained more fully hereinafter, the circuit means whereby each one of these line registers is positioned comprises ,a

.bridge including the resistors associated with dred lamps 60I arranged in ten horizontal and ten verical rows and numbered in the same order as the lamps in the field 20I of switch 200. Similarly, the image field 602 comprises one hundred image areas arranged in ten horizontal and ten vertical rows and numbered in correspondence with the numbering of the lamp field. The beam for the controller 600 is produced by an electron emitting cathode 603 and is driven by a driving mechanism 604 over the image field 602 in synchronism with and in acordance with the same pattern traced by the beam of switch 200. To this end the oscillator 605 is driven in synchronism with oscillator 2| 0, or, if desired, a common source of driving voltage may be provided. Likewise, the controller I00 is provided with a coordinate field IOI of lamps and an image field I02 arranged in the same numerical order as the fields of beam devices 200 and 600. The scanning beam of controller I00 is generated by the oathode I03 and is controlled in its scanning movement by the beam-directing mechanism I04. The driving oscillator I05 is of the same frequency and synchronized with oscillators H0 and 605, or, as above mentioned, all three devices 200, 600 and may be driven from a single source.

The function of the controller 600 is to control the vertical component of the movement of the beam of the reproducer 300. Accordingly the output voltage from the image field 602 is applied to the deflection plates 305 and 306 which determine the position of the beam in a vertical direction; and the lamps in the field 60! are connected respectively to the line registers on which the tens digits of the line numbers are registered. For example, the No. 12 lamp 606 representing line I00 is connected to the resistance bank of register 500 on which is registered the tens digit of the line paired with line I for conversation. And the No. 46 lamp 601 representing line I03 is connected to the resistance bank of line registerjf 502 on which is registered the tens digit of the subscribers line paired with line I03 for; conversation. Correspondingly the function of the controller 100 is to control the horizontal component of the movement of the beam of the reproducer 300; and the output voltage of the image field I02 is, therefore, applied to the deflection plates 301 and 308 which determine the position of the beam in the horizontal direction. The lamps in the field units digit of the subscribers line paired with line I03 for conversation.

Thus the beam devices 200, 600 and I00 are driven in synchronism over their image fields, all three of the beams'engaging at the same instant the elemental areas representing the same line. The lamps in the field L of the transmitting switch 200 represent by their varying luminosity the speech currents flowing in the lines engaged in conversation. The varying luminosity of the lamps in the field 201 is reflected on the image areas in the field 202 which in turn causes corresponding variations in the voltage applied to the grid 304 of the connecting switch 300.

' And the switch 300 translates these varying grid potentials into varying voltages applied to the subscribers lines engaged in conversation.

The intensity of illumination of the pair of lamps in the field GM of controller 600 representing each pair of lines engaged in conversation is governed by the line registers to represent the tens digits of the lines. In other words, the intensity of the lamp representing one line of a pair is a measure of the tens digit of the other line of the pair: and the same is true of the lamp representing the other line of the pair. Therefore, at the instant the beam of controller 600 engages the elemental area representing either line of the pair, the output voltage from the image field 602 is such that the beam of the connector 300 is displaced in a vertical direction by the amount representing the tens digit of the other line of the pair. Similarly, when the beams of devices 200, 600 and I00 are scanning the elemental areas representing either line of a conversational pair, the output voltage of the image field I02 is a measure of the value of the units digits of the other line of the pair and serves to deflect the beam of connector 300 in a horizontal direction by an amount corresponding to the units digit of said other line of the pair. In short, therefore, the transmitting switch 200 scans the lines in succession and repeatedly, and each time the beam engages an elemental area representing a line in conversation the beam of connector 300 is directed automatically under control of controllers 000 and I00 to the elemental area representing the other line of the pair in conversation. Since all lines are represented in the field 202 and in the field I, each calling line is connected to the associated called line and each called line'with the associated calling line once per scanning cycle. While the beam of transmitter 200is engaging the elemental area representing a line in conversation the talking currents flowing in the line are represented by the variations in the associated lamp in the field 20I and are translated through the switch 200 and the connector 300 into potentials that are applied to the other line of thepair. Two-way conversation is possible between each pair of lines, and the scanning rate of the transmitter 200 and connector 300 is so rapid with respect to the talking frequencies that the efiect is the same as though each of the pairs of lines concurrently engaged in conversation were per-' manently connected together. of pairs of lines may be engaged simultaneously in separate conversations and since the beam of the switch 300 plays over the field of elements 30I in an intricate pattern, varying from time to time as the combination of conversing lines changes, it is desirable 'to suppress the beam while it is moving from one elemental area to another and to render the beam efiective only while it is dwelling on an area to which it has been directed by the controllers 600 and I00. To this end an oscillator 2I5 is provided for controlling the suppressing grid 3I4, and'a source of negative potential 3I5 is included in circuit with said grid. The negative potential of the source 3I5 when unaffected by the oscillator 2I5 maintains the grid 3 ll at a potential sufficient to suppress the flow'of electrons from the cathode 302 to the field 30I. The oscillator 2I5, however, which is maintained in a definite phase relation with oscillators 2I0, 605 and 105, produces a voltage wave having a frequency ten times that of the oscillators 2I0, 605 and 105., The

phase relation between these oscillators is such that the positive impulses produced by the oscillator H5 and applied over conductor M6 to the grid 3 does not reach an amplitude sufiicient to overcome the battery 3I5 until the beams of switches 200, 600 and 100 have reached the selected image areas and until the output voltages from the controllers 600 and I00 have been applied to the deflection plates of the switch 300 In other words, the virtual beam of the switch 300 is driven over the field 30I and comes to rest on the desired elemental area before the operating impulse is applied by the oscillator 2I5 to the grid 3I4. When the impulse is thus applied it overcomes the negative battery 3l5, the positioned virtual beam assumes its real character, and electrons flow from the Icathode 302 to the selected elemental area under the control of the control grid 304 as above explained. The real beam of switch 300 continues to impinge upon the selected area and to transmit the talking signals to the corresponding line until the beam of switch 200 is about to move to the next elemental area in the field 202. Thereupon the positive impulse from the oscillator 2I5 ceases, and the beam of switch 300 is suppressed and assumes its virtual character. As soon thereafter as the beams of the switches 200, 600 and I00 reach the next elemental area representing a line in con-- versation, the virtual beam of switch 300 is driven from whatever position it occupies at the time to the elemental area in the field 30I corresponding to the other line involved in the conversation,

' the positive impulse is then applied by the oscillator 2I5, and the beam of switch 300 becomes real and transmits the conversational signals to said other line. Thus the beam of switch 300 assumes a virtual state during the brief intervals in which it is being driven by the controllers 600 and over the field 30 I, to prevent interference Since a plurality level representing the units digit 6."

I with otherlines that may be involved in conver- I "the operation of the system. Assume that the subscriber of line I having the designation 12 desires to converse with the subscriber of line I03 havingthe designation 46. .The initiation of the call .by the calling-subscriber results in the closure of a circuit from battery through the right winding of line relay I06,transformer coil I01, conductor I08 thence'over the substation loop and returning overcondu'etor I00, coil 0 through the left winding of. relay I06 to ground. Relay I06, which is .slow to release in character, attracts its armatures and applies ground potential to the usual line finder start conductor I I I. This start condition on conductor III causes an idle line finder 400 to operate in ing, contact of. relay II4 to ground at the inner left armature and front contact or relay 5. Relay, II5 opensthe start conductor H6 and applies ground potential to conductor M5 to render the line I03 busy in the banks of the connector switches.

its vertical and rotary movements to seize the calling line I00. When the finder reaches the calling line, a circuit is closed from battery through the winding of cut-off relay II2, closed contacts of line relay I06, normal contacts of relay II2, conductor 401, terminal andbrush of the line finder 400 to conductor 406. \The application of battery potential to conductor 406 serves in any well-known manner to terminate the hunting movement of the finder, whereupon ground potential is applied to conductor 406 in the line finder to cause the operation of the cut-off relay II2. Before its operating circuit is opened the cut-ofi relay II 2 closes a locking circuit for itself traceablefrom battery through the winding of said relay, closed contacts of relay I 06 to ground at the inner leftarmature and front contact of relay II2. Relay H2 at its outerleft armature opens the start conductor III to prevent the starting of another line finder and at its inner left armature removes'the hunting condition from conductor 40'! extending to the line finder switches. I

The calling subscriber now proceeds to manipulate his dial II3 to transmit first the tens digit 4 and then the units digit "6 of the called line I03. The impulse circuit for this purpose may be traced from battery through the lower winding of impulse relay 408, brush and terminal of line finder 400, conductor 409.conductor I08,

thence over the loop of the calling substation and returning over conductor I09, conductor 4I0, terminal and brush of line finder 400 through the upper winding of relay 408 to ground. In the well-known manner the impulse'relay 408 responds to these series of impulses to operate the connector switch 40I in a vertical direction to the level representing the tens digit 4 and in a rotary direction to a set of terminals in the connector 40I positions its uppermost set of brushes on the terminals of the called'line I03, the ringing and control mechanism 4| I associated with the connector applies ringing current in the well-known manner over conductors 2 and M3 to the called line I03. The response of the called subscriber causes the disconnection of ringing a. circuit traceable from battery through its windcalled lines respectively. The line finder 40I comes torest with its vertical commutator brush 4I6on the No. 1 terminal M1 and with its rotary commutator brush 4 I8 on the No. 2 terminal4l9; and the connector switch 40I comes to rest with its vertical commutator brush 420 on the No. 4

terminal HI and with its rotary commutator brush 422 on the No. 6 terminal 423. With these vertical and rotary commutator brushes in position, the line registers 500 and BM of the calling line I00 are set respectively in accordance with the tens andunits digits of the called line I03, and the registers 502 and 503 of the called line I03 are positioned in accordance'with the tens and units digits of the calling line I00. One half of the electrical bridge circuit for setting the register 500 may be traced. from battery 424, fixed resistor 425, brushand terminal of the finder 400, conductor 426, fixed resistor 5I0 to ground. The other half of the bridge may be traced from battery 424, connector brush 420, I

terminal 42I, graduated resistor 421, conductor 428, brush and terminalof finder 400, conductor 429, inner back contact of relay 5II, brush 504' in whatever position it may occupy at the time, through the associated graduated resistor, conductor 5|2, outer back contact oi. relayyiII to ground. Usually the bridge thus established is in an unbalanced condition and a voltage drop exists across conductors 426 and 429. Current the driving pulley 509. In either case the brush When the v5M is driven over the bank of graduated resistors until it reaches the resistor 5I4, bringing the bridge into balance and terminating the movement of the brush 504. Since the bridge is now in balance, relay 5I3 releases and closes the following operating circuit for relay 5H: battery through the winding of relay 5, normal contacts of relay 5I3, conductor 5I5 to ground at the closed contacts of the out-ofl relay II2 oi the calling line I00. Relay 5 attracts its armatures and establishes a circuit forlighting the lamp 606 representing the calling line I00 in the controller 600. This circuit may be traced from battery through the front contacts of relay 5| I, brush 504, resistor 5| 4, conductor I5I2, front contacts of relay 6| I, conductor. 5I6 through the lamp-606 to ground. Since the graduated resistor 5I4 has a. value representative of the tens digit 4, the lamp 606 burns with 'a corresponding degree of luminosity.

The bridge circuit for. setting the register. 50I may be traced from battery430 through fixed resistor m, brushand terminal of line finder 400, conductor 432, fixed resistor 511 to ground; and from battery 430, brush 422, terminal 423, associated resistor 433, conductor 434, brush and terminal of finder 400, conductor 435, normal contacts of relay 518, brush 519 and the associated resistor, conductor 520, normal contacts of relay 518 to ground. If the bridge is in an unbalanced condition, relay 521 operates, and the coil of register 501 is energized in one direction or the other to cause the movement of the brush 519 to select the graduated resistor 522, thus bringing the bridge into balance. Thereupon relay 521 releases, and relay 518 operates in a circuit from battery through its winding,

contacts Of relay 521, conductor 523 to ground at the contacts of cut-off relay 112. Relay 518 operates and closes a circuit for lighting the lamp 106 representing the calling line 100 in the controller 100. This circuit may be traced from battery through the front contact of relay 518, brush 519, graduated resistor 522, conductor 520, conductor 524, lamp 106 to ground. Since the resistor 522 represents the No. 6 units digit the lamp 106 burns with a corresponding intensity.

From an inspection of the circuits it will be found that the registers 502 and 503 of the called line 103' are. positioned to select the graduated resistors 525 and 526, under control of the commutators 402 and 403 of the finder switch 400, in accordance with the tens and units digits respectively of the calling line 100. The bridge circuit for setting the register 502 includes the fixed resistors 436 and 521 and the graduated resistor 431 as well as the resistor 525. The bridge circuit for setting the register 503 includes the fixed resistors 438 and 528 and the graduated resistor 439 as well as the resistor 526. After register 502 has been positioned, relay 52.9 operates in a circuit from battery through it's winding, normal contacts of relay 530, conductor 531 to ground at the closed contacts of cut-off relay 115. Relay 529 closes a circuit for the lamp 601 representing the called line 103 in the controller 600. The lamp circuit may be traced from-battery through the front contacts of relay 529,

' brush 532, resistor 525, conductor 533, front cona corresponding intensity. When the register F 503 is fully positioned, relay 535 operates over a circuit traceable from battery through its winding, normal contacts of relay 531, conductor 538 to ground at the front contacts of relay 115 and closes an obvious operating circuit for the lamp 101 representing the called line 103 in the controller 100. Since the resistor 526 has a value representative of the No. 2 units digit, the lamp 101 is lighted to the corresponding intensity.

Thus, following the setting of the line finder 400 and the connector 401, the line registers 500, 501, 502, 503 are positioned in accordance with the values of the digits of the lines to be engaged in conversation. Having determined the setting of the line registers. the line finder 400 and associated connector 401 may be restored to their normal condition by any suitable controlling and releasing means. These switches may now be used to serve other calls. the cut-off relays 112 and 115 are held in their operated condition under the control of the associated line relays, which in turn are held by the subscribers lines; and the operated cut-oil relays hold open the finder hunting circuits of lines 100 and 103 and also maintain these lines in a busy condition in the banks of the switches. Furthermore, the operated cut-off relays 112 and 115 maintain the relays 511, 518, 529 and 535 in their operated condition to hold the lamp circuits of the controllers 600 and 100.

The talking transmission circuits will now be explained. The calling line 100 is represented by the lamp 211 in the field 201 of the transmitter 200, and the circuit for this lamp may be traced from battery through the transformer winding 111, closed contacts of relay 112, conductor 118, lamp 211 to ground. Similarly the called subscribe'rs line 103 is represented in the field 201 by lamp 212, the circuit of which is closed from battery, through the transformer winding 119 and the front contacts of cut-off relay 115. While the calling subscriber is speaking, the varying talking currents flowing in the line 100 cause the induction in transformer winding 111 of voltages which in turn cause currents varying correspondingly to fiow through lamp 211. And the same is true with respect to line 103 and its lamp 212. Therefore, the intensity with which lamps 211 and 212 are lighted varies in accordance with the speech currents flowing in the lines 100 and 103, from which it follows that the intensity of the light images on the elemental areas 213, 214

varies in accordance with said speech currents.

As the beams of devices 200, 600 and 100 move in synchronism over the image fields, they first encounter the image areas representing the calling line 100. That is to say, the beam of switch 200 encounters the image area 213, the beam of controller 600 encounters the image area 608, and the beam of controller 100 encounters the image area 108, all at the same instant. Since the area 608 is illuminated by lamp. 606 to an intensity equivalent to the digit 4" the output voltage from the image field 602, which is amplified by amplifier 609 and applied to the control elements 305 and 306, causes the beam of the connector 300 to move vertically until it is in line with the fourth horizontal row of elements, counting from the top of the field 301. Also since the elemental area 108 in controller 100 is illuminated by lamp 106 to an intensity equivalent to the digit 6 the output voltage from the field 102, which is amplified by the amplifier 109 and applied to the control elements 301 and 308, causes the connector beam 300 to move horizontally until it is in line with the sixth vertical row of elements in the field 301, counting from the As above explained,

left. Thus the joint action of controllers 600 and brings the connector beam into engagement with the elemental area 309, representing on the grid 304 are reflected in the intensity of the electron beam impinging on the area 309, and this elemental area sets up a voltage in the conductor 311 which varies correspondingly. The varying voltage on conductor 311 causes a current of corresponding variations to flow through the transformer coils 120. These variations are in turn induced in the associated coils in the subscriber's line 300, and the speech currents flow over the conductors of said line.

Later in the scanning cycle the beams encounter the image areas 2H, 6H) and H representing the called line I03. In this case the image areas BIO and H0 are illuminated to intensities corresponding to digits 1 and 2, and the output voltages of the fields 602 and 102 cause the beam of reproducer 300 to impinge upon the elemental area 312 which is individual to the calling subscribers line I00. If at this instant the called subscriber is speaking, the output voltage of the tansmitter field 202, which is varying in accordance with his speech, is impressed upon the control grid 304, the beamof the connector 300 is varied accordingly, and the output voltage from the elemental area 3I2 causes a current of corresponding variation to fiow over conductor 3l3 through the transformer coils l2l'. The voltages across the coils l2! are induced into the subscribers line I00 and cause the fiow of speech currents therein.

Thus for each scanning cycle of the'transmit ting switch 200 a communication connection is established between the calling line I00 and the called line I03 and a separate communication connection between the called line and the callingline, and the scanning cycles are repeated at such high velocity that these communication connections for two-way conversation are to all intents and purposes permanent connections; And it will be obvious that any number of pairs of lines may be engaged in conversation concurrently.

When the subscribers have finished talking, they replace their receivers on the switchhooks, the line relays I06 and H4 release, and these relays in turn release the cut-off relays H2 and H5. The cut-off relays release the register control relays 5| I, 5H3, 529 and 535 to open the lamp circuits of the controllers 600 and 100. Thus the equipment used on this particular call is fully released and may be taken again for a subsequent call.

As previously mentioned, the beam devices 200, 600 and 100 and the reproducer 300 may be of any suitable and well-known type. Also the lamps-in the fields 20!, 60! and 1M may be chosen in accordance with the specific requirements. In particular they should be capable of varying their luminosity in accordance with the intensity of the current supplied to them. If desired light valves may be used instead of individual lamps for supplying the variable light intensity.

What is claimed is: I

1. The combination with a group of lines of means for establishing communicative connection between a pair of said lines including any one of said lines and any other one of said lines, said means comprising a device for causing a beam of energy to scan repeatedly the lines of said group, a second beam of energy, and means effective each time said first beam encounters one of the lines of said pair for directing the second beam to the other line of said pair.

2. The combination with a group of lines of means for establishing communicative connection between any pair of said lines comprising a v means for establishing communicative connection between any pair of said lines comprising means for causing a beam of energy to scan said group of lines repeatedly, a second beam of energy for making communicative engagement with the lines of said group, and means operative when said first beam scans one of the lines of. said pair for moving the other of said beams to engage the other line of said pair.

4. In a communication system, a group of lines, 'means for enabling simultaneous communication between a plurality of pairs of said lines, each pair of which may comprise any line of the group and any other line of said group, means for establishing communicative connection between the lines of each of said pairs comprising a device for causing a beam of energy to scan repeatedly the lines of said group, a second beam of energy for engaging the lines of said group, and means effective each time the first one of said beams engages one of the lines of each pair for directing the second beam into engagement with the other line of such pair.

5. In a communication system, a group of lines, means for enabling simultaneous communication between a plurality of pairs of said lines, each pair of which may comprise any line of the group and any other line of said group, means for establishing communicative connection between the lines of each of said pairs comprising a device for causing a beam of energy to scan the lines of said group repeatedly and in a definite sequential order, a second beam of energy for selectively engaging the lines of said group, and means efiective each. time said first beam encounters one of the lines of any pair for moving said second beam automatically and I directly to the other line of such pair.

6. In a communication system, a group of lines of which any line may be a calling line and any other line a called line, means for registering the designations of the calling and called lines, means for establishing a communicative connection between the calling and called lines comprising means for causing a beam of electrons to scan repeatedly the lines of said group, a second beam of electrons for selecting the lines of said group, and means controlled in accordance with the registered designations and efiective each time one of said beams encounters the calling line for directing the otherof said beams into engagement with the called line.

'7. The combination with a group of lines, a field of sensitive elements representing respectively the lines of said group, means for establishing communicative connection between any pair of said lines comprising means for causing a beam of energy to move over the sensitive elements in said field, a second field of elements representing respectively the lines of said group, means for causing a second beam of energy to move overthe elements of said second field, and

means eifective whenever said first beam encounters the element representing one of the lines of said pair in said first field for directing said second beam automatically into engagement with the element in the second field representing the other line of said pair.

8. The combination with a group of. lines of means for establishing communicative connection between any pair of said lines comprising a common register device for registering the digits of the lines of said pair, individual registers for said digits, means for transferring the registered digits from said common register device to said .10. fIn-com'bination, a group of of elements'in which said lines appear respectively, a beam of energy for said first field, a beam "of energy for said second field, means for causindividual registers, means eflective thereupon for releasing said common register device,.meansfor causing abeam of energy to scan repeatedly the lines of said group, a second beam of energy, and means controlled by said individual registers and efiective each time said first beam encounters one of the lines of said pair for directing said second beam to the other line of said pair. I

9. The combination with a group of lines of means for establishing communicative connection between any pair. of said lines comprising a "lines of said pair for directing said second beam to, the other line of 'said pair.

lines, two fields ing said first beam to traverse in repeated cycles the elements'in said first field to establish a communicative connection with any desired line at each cycleandmeans effective each time the first beam encounters the element representing the'said desired line for causing said second beam to engage the element in said second field representing any other desired line to establish communicative connection between said first and sec- ,ond desired lines.

11. In combination, two fields of elements, a group of lines, each line being represented by one of the elements in each of said fields, means for I establishing coexisting connections between a plurality of pairs of said lines comprising a device for scanning one of said'fields with an electron beam, a second device for selecting theelements in the other of said fieldswith an electron beam,

and means efiective when the first one of said beams engages theelement representing one line of a pair involved in a connection for directin the other beam to the element representing the other line of the pair.

12. In combination, two fields of elements, a group of lines, each line being represented by one of the elements in each of said fields, means for establishing coexisting connections between a plurality of pairs of said lines comprising a device for causing a beam of electrons to move repeat edly and rapidly over the elements of said first field which represent lines in a condition of communication, a second device for causing a beam to move over the second field of elements, and means effective when one of said beams engages the element representing one line 'of a pair involved in a communicative connection for causing the other beam to move directly to the element representing the other line of the pair.

13. In combination, a group of lines of which anypair may be engaged in communication, a field of lights in which said lines appear respectively, means for varying the intensity of the lights representing said pair of lines in accordance with the communication signals flowing in said lines, a field of sensitive elements, means for producing an image of said light field on said beam of energy into selective .engagement with.

field of sensitive elements, means for causing a beam of energy to scan said field of sensitive elements, and means efiective when said beam encounters the element corresponding to one line of said pair for establishing a communicative connection with the other line of said pair.

14. Th method ofestablishing a'communicative connection between the lines of a group of lines which comprises repeatedly scanning the lines 01' said group in rapid succession with a beam of energy and auomatiglly directing a second one of the lines of any pairoi lines whensaid first beam engages the other line of said pair.

15. The method of establishing communicative connections between the lines of a groupwhich comprises repeatedly scanning the lines of said group in a definite sequential order and an rapid succession with a beam of energy and directing a second beam of energy selectively into communicative connection with one of the lines of second beam of energy selectively into communicative engagement with one or the lines of each of said pairs when said first beam of energy engages the other line of such pair.

17. In combination, a plurality of lines, means for establishing a communicative connection between a pair of said lines comprising means'for causing a connecting beam of energy to scan said lines repeatedly, means for causing a second connecting beam of energy to engage said lines, an auxiliary beam of energy, and means controlled by said auxiliary beam each time one of said connecting beams makes communicative engagement with one of the lines of said pair for directing the otherof said connecting beams into communicative engagement with the other line of said pair.

I 18. In combination, a plurality of lines, means for establishing a communicative connection be-' tween a pair of said lines comprising means for causinga connecting beam of electrons to scan said lines repeatedly, means for causing a second connecting beam of electrons to engage said lines, an auxiliary beam of electrons movable in synchronism with said first connecting beam, and means controlled by said auxiliary beam each time said first connecting beam makes communicative engagement with either one of the lines of said pair for directing sai cond connecting beam into communicatl've m g gement with the other line of said pair.

19. In combination, a plurality of lines, means 1 for establishing a communicative connection between any pair of said lines comprising means for causing a beam of electrons to'scan said lines repeatedly, means for causing a second beam of electrons to engage said lines, a plurality of auxiliary beams of electrons movable in synchronism 

